Since 2007, concerns about plastic litter in the oceans have led nearly 150 California localities to pass ordinances to ban single-use plastic grocery bags and require stores to charge customers 10 cents each for carryout bags made of paper or heavier plastic. Now voters will decide if a statewide ban on the bags, passed in 2014, will go into effect or not.

Proposition 67 is a referendum on Senate Bill 270, a law proponents say is needed to protect marine wildlife from fatally ingesting plastic in the water. This is misleading.

A 2014 study of plastic litter in the world’s oceans found that plastic fishing gear accounted for most of the problem. Plastic bags and plastic film, combined, accounted for less than 10 percent of plastic items, 0.8 percent by weight. It simply isn’t true that grocery bags are a major component of ocean litter.

It makes more sense to clean up litter than to ban a useful product, but advocates of the bag ban want to communicate the message that we all have an impact on the environment and should reuse bags to generate less waste. The 10-cent fee for carryout bags, proponents of Prop. 67 told the editorial board, helps consumers “internalize” that message.

The heavier plastic and paper bags are more costly to manufacture and transport than single-use plastic bags. They’re bulkier in landfills when discarded. Taking into account the energy and water used in manufacturing, the diesel fuel used in trucking, and greenhouse gas emissions, the environmental impact of the bag ban is, at best, a mixed bag.

Laws shouldn’t be used to send a message. The editorial board recommends a no vote on Proposition 67 on Nov. 8.